1. Field of the Invention
The present invention relates to a selector circuit which receives multiple input voltages, selects one of the input voltages thus received, and outputs the voltage thus selected.
2. Description of the Related Art
In recent years, electronic devices are known that receive power supply voltage from an external power supply and charge a built-in secondary battery using the power supply voltage. In some cases, such an electronic device includes multiple power supply input terminals for receiving the external power supply. For example, a cellular phone terminal includes a power supply input terminal for a cradle (desktop holder) and another power supply input terminal for an adapter, separately.
Such an electronic device requires a selector circuit which selects one of the power supply voltages supplied to the multiple power supply input terminals, and outputs the voltage thus selected to a charging circuit. For example, a technique is disclosed in Patent document 1, in which two diodes are provided such that the cathodes are connected to each other in the form of a common terminal, and the anodes of the two diodes are used as the power supply input terminals.
With such a circuit, the highest voltage is selected from among multiple power supply voltages, and the highest voltage thus selected is output. Furthermore, in a case in which a voltage is applied to one power supply input terminal and the other power supply input terminal is grounded, such a circuit prevents reverse current flow.    [Patent Document 1]
Japanese Patent Application Laid Open No. H9-284994    [Patent Document 2]
Japanese Patent Application Laid Open No. 2002-218645
However, the circuit described in Patent document 1 has a problem in that the output voltage is reduced from that of the input voltage by the forward voltage Vf of the diode. Furthermore, in a case in which the diodes are provided in the form of external components, such a circuit has another problem of an increase in the circuit area and an increased number of components.